Today forge.typo3.org was down (internal server error) but nobody noticed it. It seems like Mongrel (http://mongrel.rubyforge.org/) didn't run anymore, so I stopped and started it again using the scripts Sebastian provided for that purpose (see /usr/local/etc/apache22/rails-scripts).

As The Forge becomes more and more important, it should be monitored and Mongrel HTTP should be started automatically in case the server has been rebooted.